Expanding-shoe drum brakes for wheeled vehicles are well know in the art--especially drum brakes that are hydraulically actuated or air actuated, in which arcuate brake shoes are pivoted about anchor members. By the use of a brake-actuating member such as a cam, the brake shoes are moved into frictional engagement with a rotating annular brake drum in order to reduce the vehicle's speed.
The brake actuating member, usually a rotatable S cam or a linear wedge, is located between adjacent ends of two pivotal brake shoes and secured to a rotatable cam shaft or a linear actuation shaft, respectively. It translates generally linear motion from a power source, such as an air motor, to move the brake shoes.
Followers, i.e., cam followers or wedge followers, which are often in the form of rollers, are rotatably fixed to the brake shoes. The actuating cam or wedge is usually located between the followers of two shoes where it can apply force simultaneously to both of the followers. Examples of such prior art cam-actuated drum brakes are in U.S. Pat. Nos. 3,497,037; 3,096,857 and 2,002,139, which are hereby incorporated by reference. While the prior art cam-actuated and wedge-actuated drum brakes, especially the S cam type, are well accepted, they are not totally satisfactory. Prior art shoe bearings are often shoe-tip types. In some of those types, a concave circular arc on each shoe (at an end of the shoe opposite the cam-actuated end), serves as a bearing. That bearing on the shoe engages an anchor pin that is mounted on an immovable spider, and the shoe rotates about the anchor pin.
A trend to the use of larger brake linings and the achievement of linings that last longer have resulted in a need for longer life of the metal portions of the brake shoes, and particularly of their bearings. Some shoe-tip bearings are not durable enough.